Heavy metal pollution affects soil ecological function.Biochar and compost can effectively remediate heavy metals and increase soil nutrients.The effects and mechanisms of biochar and compost amendments on soil nitrogen cycle function in heavy-metal contaminated soils are not fully understood.This study examined how biochar,compost,and their inte-grated use affected ammonia-oxidizing microorganisms in heavy metal polluted soil.Quan-titative PCR was used to determine the abundance of ammonia-oxidizing archaea(AOA)and bacteria(AOB).Ammonia monooxygenase(AMO)activity was evaluated by the enzyme-linked immunosorbent assay.Results showed that compost rather than biochar improved nitrogen conversion in soil.Biochar,compost,or their integrated application significantly reduced the effective Zn and Cd speciation.Adding compost obviously increased As and Cu effective speciation,bacterial 16S rRNA abundance,and AMO activity.AOB,stimulated by compost addition,was significantly more abundant than AOA throughout remediation.Cor-relation analysis showed that AOB abundance positively correlated with NO3--N(r = 0.830,P＜0.01),and that AMO activity had significant correlation with EC(r =-0.908,P＜0.01)and water-soluble carbon(r =-0.868,P＜0.01).Those seem to be the most vital factors affecting AOB community and their function in heavy metal-polluted soil remediated by biochar and compost.